Danfoss AK2-SC 255, Справочное руководство, Страница: 128 / 206

RS.8D.M1.22 AK2-SC 255 Reference Manual 127
Field limits and
units for analog
alarms
The numeric value field for an alarm based on an analog sensor (for instance, pres-
sure, temperature, humidity, and light level) will accept values from -999.9 to 999.9.
The units, which are selected in the Store Info configuration screen for Units/Lan-
guages, can be in either psi or bar for pressures, in either celsius or fahrenheit degrees
for temperature, and in either footcandles or percentage for fotocells.
The time value field will accept any numberal from 0 to 9999, and the time unit can be
seconds, minutes, or hours.
Disabling If you wish, try disabling one of the alarms just configured, or any alarm you have set
up. Then restore the alarm to the Log Only, Normal, or Critical action level. The
default settings will not appear, but rather the settings you configured. This feature
can be useful when you need to suspend only a few alarms on a rack. Remember,
though, that the alarms will not automatically return to enabled status as do alarms
suspended with the Suspend Alarms function on the service screen. (see chapter 5-2).
What alarms are
needed?
The configuration process for refrigeration, HVAC, and lighting allocates alarms for
every configured digital and analog sensor, and for each control output. Depending on
your needs, not all alarms will be useful.
F
requently
A
sked
Q
uestions FAQ #1 How do I determine what trip levels to use for high and
low suction pressure alarms?
Start by considering the target pressure that is configured for the rack. Know the
range of pressures that the rack will operate in when loads, product temperatures,
defrosts, and other factors are working correctly. Then set the alarms at the upper
(high pressure) and lower (low pressure) limits of that range. Start with conservative
settings. If your settings are too tight on one end or both, and you are getting a large
number of false alarms, make sure the system is operating safely for the product and
equipment, then extend the alarm range gradually. If you don’t ever get any false
alarms, the alarm parameters are probably too loose.
Remember that more or less temporary factors such as overloading, service, and
cleaning can cause alarms to occur. Be careful to investigate any suspicious alarm
that occurs when causative activities are going on in the store.
FAQ #2 Can you be more specific and perhaps give “thumb rules”
for alarm settings?
OK, let’s assume that this particular rack is set for a target of 14 psi and is operating
to your satisfaction with that setting. Typically we find that adding 10 psi to the target
and setting the trip level for high suction pressure at 24 psi for 30 minutes is a good
starting setting. If the suction pressure is more than 10 psi above target for a half
hour, we should suspect that something is keeping the rack from making target
pressure. One possible cause is an off-line compressor.
For the low suction pressure alarm, first look at the cut-out setpoint that has been
configured for the rack. With a target of 14 psi, perhaps the cut-out is set at 2 or 3. If